This invention relates to an orthogonal transformer and an apparatus operational thereby.
To extract spectrum information from a voice signal, a Fourier transform is generally employed. However, a Fourier transform may function as an orthogonal transformer in a trigonometrical function system, and a multiplier is therefore required to perform the transformation which complicates the hardware configuration. On the other hand, the Walsh transform is available as another means for the orthogonal transformation. As an example of applying it to the spectrum analysis of a voice signal, there is presented a report by Hidafumi Ohga et al., "A Walsh-Hadamard Transform LSI For Speech Recognition", IEEE Transactions on Consumer Electronics, Vol. CE-28, No. 3, August 1982, pp. 263 to 270. The Walsh transform is a rough approximation to the Fourier transform, wherein as a twiddle factor (called "element of matrix" otherwise when expressed in matrix, the following description employing "twiddle factor") +1 and -1 are specified on the real axis, and thus a multiplication with the twiddle factor can be replaced by an addition and a subtraction to eliminate the multiplier and also to simplify the hardware configuration. The Walsh transform is described in detail in a report, "BIFORE or Hadamard Transform" by Nasir Ahmed, IEEE Transactions On Audio and Electroacoustics, September 1971, pp. 225 to 234. However, a trigonometrical function value in the Fourier transform as the twiddle factor is quantized in the Walsh transform to .+-.1 (trigonometric function value being replaced by .+-.1), which may result in a coarse quantization and a large quantizing error, and thus an approximation of the Fourier spectrum deteriorates.